Document source of various metadata files

The cht, dat, and metadat folders contain files whose source of truth is unclear. Without knowing the source, it's hard to know if the data needs to be updated. Also, if the source is known then automatic processes could be developed to automatically keep them up to date or alternative sources could be suggested. For example, it might be interesting to replace most of the metadat files with code that scrapes a game database like screenscraper.fr or thegamesdb.net.

This documentation could be in the form of a simple README inside each specific sub-folder or a comment with a URL added to the header of the dat file.

Review the cht, dat, and metadat folders to identify the source of each file. Record each source in a README in the relevant subfolder or as a URL comment in the dat file header. Done means the files have documented sources clearly enough to guide updates or future automation, including sources such as screenscraper.fr or thegamesdb.net where applicable.